In the oil and gas industry, wellbores are drilled into the Earth's surface to access underground reservoirs for the extraction of hydrocarbons. Once drilled, a wellbore is often lined with casing, which is secured within the wellbore with cement. In one cementing technique, a cement composition is pumped through the interior of the casing to the bottom of the well and the redirected back toward the Earth's surface via the annulus defined between the wellbore wall and the casing. In another cementing technique, commonly referred to as reverse-circulation cementing, the cement composition is pumped through the annulus to the bottom of the well and then back toward the surface via the interior of the casing. Once the cement composition cures within the annulus, the casing helps stabilize the wellbore walls to prevent collapse and also isolates the various surrounding subterranean formations by preventing the flow or cross-flow of formation fluids via the annulus. The casing further provides a surface to secure pressure control equipment and downhole production equipment.
When advancing a string of casing into a wellbore filled with wellbore fluids (e.g., drilling fluid or other fluids), the casing can act as a piston as it interacts with the wellbore fluids. Hydraulic forces resulting from such interaction can damage weak formations and require lengthy run-in times. To avoid this phenomenon, auto-filling float equipment is sometimes coupled to the end of the casing. The auto-filling float equipment typically includes a flapper-type float valve that is propped open so the casing can fill with wellbore fluid from the bottom of the string as the casing is lowered into the wellbore. This decreases the load on the formation and allows for quicker run-in speeds.
Prior to cementing the casing in place, the auto-fill float equipment must be deactivated, which converts the float valve into a type of check valve. Deactivating the auto-fill float equipment is typically done by pumping a wellbore projectile (e.g., a ball or a dart) through the float valve to shift a sleeve out of propping engagement with a flapper, and thereby allowing the flapper to close. Circulation from the surface prior to deactivation of the auto-fill is oftentimes necessary, and small flow ports around a seat where the wellbore projectile lands allow fluid to flow around the wellbore projectile at low rates. The flow ports, however, are relatively small and can become packed with debris, which can cause early deactivation when circulating from the surface. Additionally, the flow ports have a tendency to erode with extensive periods of circulation, which can result in the need for unusually high deactivation flow rates.